Correct application of plaster and coloured finishes on walls and floors made of Isotex
Foreword for perfect plaster
Application of plaster must only and exclusively be applied to dry surfaces, thereby avoiding operations on walls dampened by rain, frost or for poorly hardened casts. Do not proceed with plaster application in temperatures of less than 4°C, as that would result in a considerable delay in hardening and, consequently, the application times of finishes would be considerably prolonged. A week before application of the plaster, close any gaps between the blocks caused by incorrect laying with mortar, to avoid significant thicknesses of plaster, which could become potential points of cracking.
Construction of the walls should as much as possible be plumb and square. The use of plaster to correct walls that are not square and plumb is never acceptable. A thickness of more than 2 cm leads to crack formation. Where it is necessary to apply thicknesses of plaster greater than 2 cm, it is essential that the application is carried out in two layers, after maturation of at least 28 days from the first layer.
Application of the plaster
Having given this important introduction, we more on to application of the plasterwork, pre-mixed or traditional, and considering plaster has the function of protecting the wall from bad weather and wear, it should as close as possible have a thickness of 15 mm, still keeping in mind lesser or greater thicknesses may cause crack formation.
Over the last few years, insulation is becoming ever more efficient which makes it all the more important to consider inserting a suitable mesh, in alkali-resistant fibre glass with CE marking, positioned half way through the plaster; therefore 7-8 mm from the support.
Application of external finishes
The finish (with fine mortar or other) must always be applied after a layer of adhesive once the plater has hardened, which on average occurs after at least 3-4 weeks. This interval varies according to climatic conditions. This type of finish (for outdoors), to be successful must be made with a fully matured base layer (15 mm) in order to avoid the formation of shrinkage cracks. Isotex Srl does not recommend its use given the enormous difficulties in verifying conditions and timings of application are met.
The solution we recommend is to apply on the base coat of the plaster (15mm) after the latter, in the application phase, has been levelled – a thick coloured finish, after waiting 4-6 weeks from completion of the same base coat; this solution does not include fine mortar or other. When applying the base coat and levelling with a straight edge it is important to maintain a uniform and consistent covering to avoid chalking the surface.
Isotex Srl can supply data sheets on the characteristics of these products for external finishes and their methods of application which, nevertheless, must always guarantee resistance of walls against water and to maintain low levels of resistance against the passage of vapour.
Application of interior finishes
For interiors, an interval of 4-5 days is recommended between the base plaster layer and the fine mortar (or other) in order to allow for curing the base layer well before application of the fine mortar.
It should be noted that Isotex Srl declines any liability for any future problems that might arise, given it is not able to control compliance with the above-mentioned recommendations on a daily basis, regarding the quality of the materials used (plasterwork and coloured finishes), or the timings of application.
Correct installation of Isotex floor plaster
Considering the particular aspects of S 39 floors, which for technical reasons has no concrete in the joints between panels, but which has slots. Micro-cracks might form at such joints for which the use of plasterboard is recommended to avoid such problems.
For intermediate flooring (S20, S25, S30): if a finish with plaster is chosen at a thickness of 15 mm, not less, it is recommended you “submerge” an alkali-resistant plaster reinforcement mesh, with CE marking, at half thickness. There should be a wait of 4-5 days, depending on the season, before applying the finish, and 4-6 weeks before applying the paint.
